#include<stdio.h>
#include<algorithm>
using namespace std;

#define NMAX 2000003

bool v[NMAX + 5];

int main () {
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    int n, cnt;
    cnt = 0;
    scanf("%d", &n);
    for(int i = 2; i <= n; i++) {
        if (v[i] == 0) {
           // printf("%d\n", i);
            for(long long j = (long long)i * i; j <= n; j += i)
                v[j] = 1;
        }
    }
   //return 0;
    for(int i = 2; i <= n; i++) {
        if(v[i] == 0)
            cnt++;
    }
    printf("%d", cnt);
    return 0;
}